Electricity stored and regenerated in batteries is done via reduction and oxidation occurred on cathode and anode, respectively. At present, graphite is widely used as an anode material for lithium-ion batteries for the electronic products due to the advantages of low cost, low and flat working voltage, and excellent reversibility. However, the disadvantage of graphite anode is its relatively low theoretical capacity (about 370 mAh/g or about 830 Ah/L). Thus, new anode materials are being explored by mixing tin metal with other elements (such as cobalt and carbon, etc.). Compared with graphite anode, tin anode has a specific capacity more than doubled and the overall battery capacity can be increased by 30%.
When the potential of tin metal is polarized to a sufficient low potential, tin metal is able to react with lithium ions to form an alloy and has high theoretical capability (about 993 mAh/g). However, since the severely volumetric expansion/contraction of electrode occurs during the charge/discharge (lithiation/delithiation) processes, it results in structural disruption and decreased cycle life/reversibility of electrode, and thus the commercialization of the tin metal anode material is impeded. For enhancing the cycle life/reversibility of the tin electrode and reducing the impact of the volumetric expansion/contraction thereof, pores and voids are preset in the conventional metal anode material to accommodate the required space after the metal expansion. It is the attempt to achieve the objects of increasing the entirely structural stability and cycle life/reversibility of electrode.
So far, there has been no report on making porous tin particles. U.S. Pat. No. 7,244,513 discloses that silicon powder are directly etched by the acidic solution for preparing silicon particles with porous outermost layers, where the prepared silicon particles are further manufactured as silicon nanoparticles using ultrasonic agitation. However, hydrogen fluoride and nitric acid are consumed in the etching method, and nitrogen dioxide is generated. Since an abundant amount of chemical materials are used to generate waste, the process would not conform more and more rigid environmental standards. Liu et al. (2007) indicated that the nickel (Ni) and silicon (Si) are partially reacted using planetary mill to form an intermediate phase of Ni/Si/NiSi composite, and then the unreacted Ni in the composite is dissolved with acidic solution to obtain the porous NiSi alloy particles. However, the process is complicated and elaborated, plenty of acidic wastes are generated, the manufacturing cost is high, and the environment is severely damaged.
Therefore, it is an important issue to research the preparing method of tin anode electrode while reducing the use of reaction materials and the waste production, and keeping the high capability and cycle life.
It is therefore attempted by the applicant to resolve the above situation encountered in the prior article.